430 



MINERALOGY. 



to Folk, 

 stone. 



Shake- 



apeare'a 



cliff. 



Geognosy. The following are descriptions of some chalk districts in 

 "~"~ ' England, as given by Mr. Phillips from the Geological 



Transactions. 



Descrip- " The chalk cliffs between Deal and Folkstone are ex- 

 tion of the tremely interesting. A short distance on the west of 



" Dea '' '^ halk ' W ' th numerous flints ' riscs from be ' 



neath alluvial sand, and continues to rise, constituting 

 the whole cliff for about five miles ; namely, as far as 

 St. Margaret's Bay, where the summit is about 150 feet 

 above the sea. West of that place its rise is gradual 

 ;is f;ir as the cliff above which Dover Castle stands ; 

 and the greater part of it, beneath the castle, consists 

 of the chalk with numerous flints ; but the lower part 

 of the bed is full of organic remains ; of sponges and 

 echinites, &c. of which the traces are visible on the 

 surface of the cliff, projecting from it in the form of 

 knobs, of a colour somewhat darker than the chalk it- 

 self. The beds of flint between Deal and St: Mar- 

 garet's Bay, are numerous and thin ; but between the 

 latter place and Dover they increase in thickness ; and 

 the flints are not nodular, but form beds of irregular 

 thickness, with occasional cavities. The lower part of 

 the cliff, beneath the castle, consists of chalk tvith few 

 flints, in which lie some beds of soft chalk-marl, which, 

 as it falls away by exposure, leaves crevices, by which 

 the stratification is easily traced. These crevices rise 

 from the beach, mid-way between St. Magaret's and 

 Dover, are visible beneath the castle about one-third 

 of the way up the cliff: are again seen in the cliff at 

 the back of the town at a higher elevation, and again 

 near the summit of Shakespeare's cliff on the west of 

 Dover ; proving the regular stratification of the chalk 

 and its gentle dip. The low cliff commencing on the 

 west of Dover, consists of a stratum of chalk, contain- 

 ing numerous beds of sponges, and other organic re- 

 mains, but no flints ; this bed forms the great body of 

 Shakespeare's cliff, from the base, to where it under- 

 lies the chalk with few flints near the summit, and con- 

 tinues to rise five miles westward, until, near Folk- 

 stone, where the cliff is 550 feet high, it forms the 

 the greater part of the upper half. Immediately at 

 the foot of Shakespeare's cliff, a new stratum rises from 

 the beach, consisting of chalk, also without flints, con- 

 taining few organic remains, and above 50 feet thick ; 

 it is separated from the superincumbent bed, by a bed 

 of mar), which may be seen with little interruption for 

 five miles. A little on the west of Shakespeare's cliff, 

 the grey chalk rises, and may be traced to where the 

 high cliff terminates above Folkstone. This chalk is 

 of a grey colour, is softer than common chalk, contains 

 some alumina, and the same kind of organic remains 

 as are commonly found in chalk, and some thin beds 

 of sandstone, but no flints. But it is impossible to dis- 

 cover the thickness of this body, for though the cliff 

 near Folkstone is 550 feet high, a most enormous and 

 picturesque ruin covers its base. It is, however, pro- 

 bable that the chalk there rests upon a bed of blue 

 marl, and that the giving way of this stratum has been 

 the cause of the ruin. The marl is seen lying on the 

 green sand at Copt Point near Folkstone, and at places 

 between that point and the chalk-hills. In the cliffs 

 east and west of Dover, therefore, we have all the 

 members of the chalk formation, except the marls ; 

 which, in the Isle of Wight, lie above and below the 

 chalk properly so called." 

 Chalk of The chalk of Cambridgeshire is described as con- 

 Cambridge- gisting of two varieties ; the tipper, containing the com- 

 mon black flint in abundance, and the loner or grey 

 chalk, which contain little or none. If a line be drawn 

 from Royston by Balsham to Newmarket, it will pretty 



Secondary 

 gypsum. 



*hire. 



exactly define the limits of both varieties ; the hills to Geognosy, 

 the eastward of it being composed of the upper beds, N V""* ' 

 while those to the west, consist of the lower of grey 

 chalk, which composes by far the greatest part of the 

 hills of Cambridgeshire. It is considerably harder 

 than common chalk, and its colour is usually some 

 shade of grey. Its provincial name is cliinch, and it 

 yields the best lime. Some of the beds are hard enough 

 to serve the purpose of building stone. It also en- 

 dures the fire well ; and is used, like that of Ryegate 

 and Measham in Surrey, for the backs of grates. In 

 the northern extremity of the Cambridgeshire hills, 

 the chalk appears to rest upon an extensive bed of 

 blue clay, termed gault ; but there is no decisive line 

 of separation between them ; they are considered to 

 pass into each other by degrees, the lower beds of the 

 grey chalk becoming more sandy, and assuming gra- 

 dually the nature of an argillaceous loam. In the Red chalk 

 wolds of Lincolnshire, the chalk has two colours, red of Lincoln- 

 and white, each lying in. regular strata, the red being shire, 

 generally undermost ; in the white, seams of flint are 

 frequently met with from two to six inches thick. The 

 chalk rests upon a coarse brown pebbly-sand, without 

 organic remains, consisting of quartz and oxide of 

 iron. 



V. Fifth Secondary Limestone. 



Fifth se- 



This formation is one of the members of the series condary 

 above chalk, and will be included in the description of limestone. 

 the Paris formation. 



III. Secondary Gypsum. 



Flcetz Gyps. Werner. 

 Secondary Gypsum. Jameson. 



There are two principal formations of this rock ; one 

 is associated with the rocks of the variegated or new 

 red sandstone, and the other is a member of the series 

 above chalk, or what is called the Paris formation. 



1. First, Secondary Gypsum, including Salt. 



Erster und Zweiter Flcetz Gyps, and Steinsalzgebirge. gypsum 

 Werner. 



Characters. It occurs granular, foliated, fibrous, Character!, 

 compact, in crystals (selenite,) and sometimes anhy- 

 drous. Its principal colours are white and grey, seldom 

 red or brownish. It occasionally contains imbedded 

 crystals of different kinds, such as quartz, boracite, ar- 

 ragonite, and sulphur; and sometimes disseminated, 

 and imbedded masses of clay, marl, sandstone, lime- 

 stone, sulphur, and salt. 



Subordinate beds. It contains beds of marl, clay, lime- Subordi- 

 stone, sandstone, sulphur, and salt. These beds of nate bedi. 

 salt afford the mineral salt of commerce, and are work- 

 ed in the salt mines of Cheshire, Austria, and Poland. 



Structure. It is either distinctly stratified, or is dis- s trucuire 

 posed in short but thick and unstratified beds. Caves 

 varying in magnitude from a few yards to many fathoms 

 in extent, occur in it ; and of these there are striking 

 examples in Thuringia, and in other countries. It is 

 conjectured that they owe their origin to masses of 

 salt which they formerly contained, and which have 

 been removed in the course of ages by the action of 

 subterranean waters. The magnitude of these caves Cavei. 

 is further increased by the action of percolating water 

 traversing the gypsum itself. Frequently the roofs of 

 the caves yield and fall in, and thus hollows, often fun- 

 nel-shaped, are formed in the surface of the country. 



Petrifactions. It rarely contains petrifactions; and Petrifac- 

 of these, species of the following genera have been tioni. 



First se- 

 condary 



